Travis: Put back latest nightly version of Rust compiler
Travis: Put back latest nightly version of Rust compiler

mcav/foxbox,mcav/foxbox,fabricedesre/foxbox,hkoka/foxbox,julienw/foxbox,hkoka/foxbox,hkoka/foxbox,fabricedesre/foxbox,fxbox/foxbox,cr/foxbox,Yoric/foxbox,Yoric/foxbox,aosmond/foxbox,mcav/foxbox,cr/foxbox,npark-mozilla/foxbox,cr/foxbox,aosmond/foxbox,mcav/foxbox,julienw/foxbox,npark-mozilla/foxbox,fabricedesre/foxbox,gabrielesvelto/foxbox,hkoka/foxbox,fxbox/foxbox,fxbox/foxbox,julienw/foxbox,aosmond/foxbox,cr/foxbox,fabricedesre/foxbox,Yoric/foxbox,npark-mozilla/foxbox,npark-mozilla/foxbox,fxbox/foxbox,gabrielesvelto/foxbox,gabrielesvelto/foxbox,Yoric/foxbox